Three-port converter with wide input range and control method thereof

ABSTRACT

A three-port converter with a wide input range and a control method thereof are provided, which relates to a technical field of power electronic converters. The converter is provided with three ports of a photovoltaic cell PV, a storage battery Bat and a resistance load R, and includes a boost circuit (Boost) and a reversible boost-buck circuit (Sepic-Zeta). The boost circuit is configured to connect the photovoltaic cell PV and the load R; and the reversible boost-buck circuit is configured to connect the photovoltaic cell PV, the storage battery Bat, the storage battery Bat and the load R. The three-port converter of the present disclosure has advantages of a small size, a wide input range, a high integration level, high stability, high conversion efficiency, etc.

CROSS REFERENCE TO RELATED APPLICATION(S)

This patent application claims the benefit and priority of Chinese Patent Application No. 202110701530.9 filed with the China National Intellectual Property Administration on Jun. 23, 2021, which is incorporated by reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The present disclosure relates to the technical field of energy conversion for power electronics, in particular to a nonisolated three-port direct-current switching converter based on a reversible Sepic-Zeta with a wide input range and a control method thereof.

BACKGROUND

With increasing environmental problems and a shortage of fossil energy, renewable energy power generation technologies such as solar power generation and wind power generation have attracted widespread attention. A conventional photovoltaic energy-storage power generation system generally transmits energy through a combination of multiple two-port converters, which causes problems of an excessive quantity of converters, a large size, a low power density, etc. A three-port converter can be adopted to replace the original multiple two-port converters, which enables the system to have a simpler overall structure, a smaller size, a higher power density, etc. The three-port converter can achieve power generation of new energy, energy storage and load connection and control simply through one combined converter, which therefore effectively improves efficiency and power density of the system.

However, most existing nonisolated three-port switching DC-DC converters limit the relationship between a voltage of a photovoltaic cell and a voltage of a storage battery to a certain degree. As referred to in [1] Wang Hui, Chen Yao, Zeng Qingdian, Li Shengqian, Zhu Binxin, A Multi-mode high-gain multi-port DC/DC converter [J]. Proceedings of The Chinese Society for Electrical Engineering, 2019,39(07):2155-2166, the three-port converter is only suitable for an application scenario where a voltage V_(pv) of the photovoltaic cell is less than a voltage V_(B) of the storage battery, and in [2] Suresh, K. , et al. “Cost-efficient nonisolated three-port DC-DC converter for EV/HEV applications with energy storage.” European transactions on electrical power engineering 29.10(2019):e12088.1-e12088.20., the three-port converters is only suitable for an application scenario where the voltage V_(pv), of the photovoltaic cell is greater than the V_(B). The mutually-limiting relation between the voltage of the photovoltaic cell and the voltage of the storage battery causes a narrow application range, poor stability, and low conversion efficiency, thereby affecting the performance of the converter during long-term use.

SUMMARY

To overcome the shortcomings in the conventional art, the present disclosure provides a three-port converter with a wide input range and a control method thereof. The three-port converter has advantages of a small size, a wide input range, a high integration level, high stability, high conversion efficiency, etc.

The technical solutions of the present disclosure are as follows.

A three-port converter with a wide input range and a control method thereof are provided. The converter is provided with three ports of a photovoltaic cell PV, a storage battery Bat, a resistance load R, a boost circuit (Boost) and a reversible boost-buck circuit (Sepic-Zeta). The boost circuit is configured to connect the photovoltaic cell PV and the load; and the reversible boost-buck circuit is configured to connect the photovoltaic cell PV, the storage battery Bat, the storage battery Bat and the load R. Specifically, in the boost circuit (Boost), a positive electrode of the photovoltaic cell PV is connected to an end of a capacitor C₁ and an anode of a diode VD₁, and an anode of a diode VD2 is connected to an end of an inductor L₁; a drain of a switching tube S₄ and an anode of a diode VD₄ are connected to an other end of the inductor L₁; a cathode of the diode VD₄ is connected to an end of an output filtering capacitor C₄ and an end of the load R; in the boost-buck circuit (Sepic-Zeta), a positive electrode of the storage battery Bat is connected to an end of a capacitor C₂ and an end of an inductor L₂, a drain of a switching tube S₂ and an end of a capacitor C₃ are connected to an other end of the inductor L₂, three branches are led out from an other end of the capacitor C₃ with the first branch connected to a source of a switching tube S₁, the second branch connected to a drain of a switching tube S₃, and the third branch connected to an end of an inductor L₃, a series circuit of the switching tube S₁ and the diode VD₂ is connected to a cathode of the diode VD₁ and the end of the inductor L₁, and a series circuit of the switching tube S₃ and a diode VD₃ is connected to the other end of the inductor L₂ and the anode of the diode VD₄; and the cathode of the diode VD₄ is connected to the end of the output filtering capacitor C₄ and the end of the load R; and an other end of the load R is connected to an other end of the output capacitor C₄, a source of the switching tube S₄, an other end of the inductor L₃, a source of the switching tube S₂, the other end of the capacitor C₂, a negative electrode of the storage battery Bat, an other end of the capacitor C₁, and a negative electrode of the photovoltaic cell PV.

The present disclosure further provides a nonisolated three-port direct-current switching converter based on a reversible Sepic-Zeta and with a wide input range and a control method thereof, the control method including following four operating modes which are specifically described as follows:

(1) an operating mode of a photovoltaic cell PV supplying power to a load R and charging a storage battery Bat:

in a case that neither a switching tube S₂ nor a switching tube S₃ operates, when a switching tube S₁ and a switching tube S₄ are turned on, the photovoltaic cell PV charges the storage battery Bat via a capacitor C₃ and an inductor L₂, and charges the inductor L₂ and an inductor L₃; when the switching tube S₁ is turned off and the switching tube S₄ continues to be turned on, the photovoltaic cell PV continues to charge an inductor L₁, the inductor L₃ charges the capacitor C₃, and the inductor L₂ supplies power to the load via freewheeling through a body diode of the switching tube S₂; when the switching tube S₄ and the switching tube S₁ are both turned off, the photovoltaic cell PV and an inductor L₁ charge the load, the inductor L₃ continues to charge the capacitor C₃, and the inductor L₂ continues to supply power to the load via freewheeling through a body diode of the switching tube S₂;

(2) an operating mode of the photovoltaic cell PV and the storage battery Bat jointly supplying power to the load R:

when a voltage V_(pv) of the photovoltaic cell is greater than a voltage V_(B) of the storage battery, the switching tube S₁ does not operate, and the switching tube S2 and the switching tube S3 are turned on complementarily; when the switching tube S₂ is turned on and the switching tube S3 and the switching tube S4 are turned off, the photovoltaic cell PV and an inductor L₁ supply power to the load R, the storage battery Bat charges the inductor L₂, and the capacitor C₃ charges the inductor L₃; when the switching tube S₂ continues to be turned on, the switching tube S3 continues to be turned off, and the switching tube S₄ is turned on, the photovoltaic cell PV charges the inductor L₁, the storage battery Bat continues to charge the inductor L₂, and the capacitor C₃ continues to charge the inductor L₂; when the switching tube S₃ is turned on and the switching tube S₂ and the switching tube S₄ are turned off, the photovoltaic cell PV and the inductor L₁ supply power to the load R, the storage battery Bat and the inductor supply power to the load via the capacitor C₃, and the inductor L₃ also supplies power to the load R;

when the voltage V_(pv) of the photovoltaic cell PV is smaller than the voltage V_(B) of the storage battery and a duty ratio of the switching tube S₂ is smaller than that of the switching tube S₄, the switching tube S₁ does not operate; when the switching tube S₄ is turned on and the switching tube S2 and the switching tube S3 are turned off, the photovoltaic cell PV charges the inductor L₁; when the switching tube S₄ continues to be turned on continuously, the switching tube S₃ continues to be turned off, and the switching tube S₂ is turned on, the photovoltaic cell PV continues to charge the inductor L₁, the storage battery Bat charges the inductor L₂, and the capacitor C₃ charges the inductor L₃; when the switching tubes S₂ and S₄ are turned off and the switching tube S₃ is turned on, the photovoltaic cell PV and the inductor L₁, the storage battery Bat and the inductors L₂ and L₃ supply power to the load R simultaneously;

(3) an operating mode of the storage battery Bat separately supplying power to the load R:

in a case that neither the switching tube S₁ nor the switching tube S₄ operates, the switching tube S₂ and the switching tube S₃ are turned on complementarily, and input power of the photovoltaic cell PV is zero; when the switching tube S₂ is turned on and the switching tube S₃ is turned off, the storage battery Bat charges the inductor L₂, and the capacitor C₃ charges the inductor L₃; when the switching tube S2 is turned off and the switching tube S₃ is turned on, energy in the storage battery Bat and the inductors L₂ and L₃ is supplied to the load R via the switching tube S₃; and

(4) an operating mode of the photovoltaic cell PV separately supplying power to the load R:

in a case that none of the switching tube S₁, the switching tube S₂ and the switching tube S₃ operate, when the switching tube S₄ is turned on, the photovoltaic cell PV charges the inductor L₁, and when the switching tube S₄ is turned off, the photovoltaic cell PV and the inductor L₁ simultaneously supply power to the load R.

Compared with the conventional art, the present disclosure achieves the following beneficial effects.

The present disclosure achieves a wide input voltage range, the photovoltaic cell PV and the storage battery Bat are connected via the reversible boost-buck circuit (Sepic-Zeta), such that the three-port converter operates not only in a case that the voltage V_(pv) of the photovoltaic cell is greater than the voltage V_(B) of the storage battery, but also in a case that voltage V_(pv) of the photovoltaic cell is smaller than the voltage V_(B) of the storage battery. The three-port converter of the present disclosure further has the advantages of a small size, a high integration level, high stability, high conversion efficiency, etc.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a topology of a nonisolated three-port direct-current switching converter according to the present disclosure;

FIG. 2 is an equivalent circuit diagram illustrating an operating process of a photovoltaic cell PV supplying power to a load R and charging a storage battery Bat according to the present disclosure;

FIG. 3 is an equivalent circuit diagram illustrating an operating process of the photovoltaic cell PV and the storage battery Bat jointly supplying power to the load R according to the present disclosure;

FIG. 4 is an equivalent circuit diagram illustrating an operating process of the storage battery Bat separately supplying power to the load R according to the present disclosure;

FIG. 5 is an equivalent circuit diagram illustrating an operating process of the photovoltaic cell PV separately supplying power to the load R according to the present disclosure;

FIG. 6 is an operating waveform diagram illustrating the photovoltaic cell PV supplying power to the load R and charging the storage battery Bat according to the present disclosure;

FIG. 7 and FIG. 8 are operating waveform diagrams illustrating the photovoltaic cell PV and the storage battery Bat jointly supplying power to the load R according to the present disclosure;

FIG. 9 is an operating waveform diagram illustrating the storage battery Bat separately supplying power to the load R according to the present disclosure; and

FIG. 10 is an operating waveform diagram illustrating the photovoltaic cell PV separately supplying power to the load R according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions of the present disclosure are described in detail below with reference to the drawings.

A three-port converter with a wide input range according to the present disclosure, as shown in FIG. 1 , is provided with three ports of a photovoltaic cell PV, a storage battery Bat, and a resistance load R, and includes a boost circuit (Boost) and a reversible boost-buck circuit (Sepic-Zeta), where the boost circuit is configured to connect the photovoltaic cell PV and the load, and the reversible boost-buck circuit is configured to connect the photovoltaic cell PV, the storage battery Bat, the storage battery Bat and the load R. Specifically, in the boost circuit (Boost), a positive electrode of the photovoltaic cell PV is connected to an end of a capacitor C1 and an anode of a diode VD1, and an anode of a diode VD2 is connected to an end of an inductor L1. A drain of a switching tube S4 and an anode of a diode VD4 are connected to an other end of the inductor L1; a cathode of the diode VD4 is connected to an end of an output filtering capacitor C4 and an end of the load R; in the boost-buck circuit (Sepic-Zeta), a positive electrode of the storage battery Bat is connected to an end of a capacitor C2 and an end of an inductor L2, a drain of a switching tube S2 and an end of a capacitor C3 are connected to an other end of the inductor L2, three branches are led out from an other end of the capacitor C3 with a first branch connected to a source of a switching tube S1, a second branch connected to a drain of a switching tube S3, and a third branch connected to an end of an inductor L3, a series circuit of the switching tube S1 and the diode VD₂ is connected to a cathode of the diode VD1 and the end of the inductor L1, and a series circuit of the switching tube S3 and a diode VD3 is connected to the other end of the inductor L2 and the anode of the diode VD4. The cathode of the diode VD4 is connected to the end of the output filtering capacitor C4 and the end of the load R; and an other end of the load R is connected to an other end of the output capacitor C4, a source of the switching tube S4, an other end of the inductor L3, a source of the switching tube S2, the other end of the capacitor C2, a negative electrode of the storage battery Bat, an other end of the capacitor C1, and a negative electrode of the photovoltaic cell PV.

The present disclosure further provides a control method of a three-port converter with a wide input range, the control method including the following four operating modes as specifically described below.

(1) An operating mode of the photovoltaic cell PV supplying power to the load and charging the storage battery Bat:

In a case that neither the switching tube S2 nor the switching tube S3 operates, when the switching tube S1 and the switching tube S4 are turned on, the photovoltaic cell PV charges the storage battery Bat via the capacitor C3 and the inductor L2, and charges the inductor L2 and an inductor L3; when the switching tube S1 is turned off and the switching tube S4 continues to be turned on, the photovoltaic cell PV continues to charge the inductor L1, the inductor L3 charges the capacitor C3, and the inductor L2 supplies power to the load via freewheeling through a body diode of the switching tube S2; when the switching tube S4 and the switching tube S1 are both turned off, the photovoltaic cell PV and the inductor L1 supply power to the load, the inductor L3 continues to charge the capacitor C3, and the inductor L2 continues to supply power to the load via freewheeling through the body diode of the switching tube S2.

(2) An operating mode of the photovoltaic cell PV and the storage battery Bat jointly supplying power to the load R:

When a voltage Vpv of the photovoltaic cell is greater than a voltage VB of the storage battery, the switching tube S1 does not operate, and the switching tube S2 and the switching tube S3 are turned on complementarily; when the switching tube S2 is turned on and the switching tube S3 and the switching tube S4 are turned off, the photovoltaic cell PV and the inductor L1 supply power to the load R, the storage battery Bat charges the inductor L2, and the capacitor C3 charges the inductor L3; when the switching tube S2 continues to be turned on, the switching tube S3 continues to be turned off, and the switching tube S4 is turned on, the photovoltaic cell PV charges the inductor L1, the storage battery Bat continues to charge the inductor L2, and the capacitor C3 continues to charge the inductor L2; when the switching tube S3 is turned on and the switching tube S2 and the switching tube S4 are turned off, the photovoltaic cell PV and the inductor L1 supply power to the load R, the storage battery Bat and the inductor supply power to the load via the capacitor C3, and the inductor L3 also supplies power to the load R;

when the voltage Vpv of the photovoltaic cell PV is smaller than the voltage VB of the storage battery and a duty ratio of the switching tube S2 is smaller than that of the switching tube S4, the switching tube S1 does not operate; when the switching tube S4 is turned on and the switching tube S2 and the switching tube S3 are turned off, the photovoltaic cell PV charges the inductor L1; when the switching tube S4 continues to be turned on, the switching tube S3 continues to be turned off, and the switching tube S2 is turned on, the photovoltaic cell PV continues to charge the inductor L1, the storage battery Bat charges the inductor L2, and the capacitor C3 charges the inductor L3; when the switching tubes S2 and S4 are turned off and the switching tube S3 is turned on, the photovoltaic cell PV, the inductor L₁, the storage battery Bat and the inductors L2 and L3 supply power to the load R simultaneously.

(3) The operating mode of storage battery Bat separately supplying power to the load R:

In a case that neither the switching tube S1 nor the switching tube S4 operates, the switching tube S2 and the switching tube S3 are turned on complementarily, and input power of the photovoltaic cell PV is zero; when the switching tube S2 is turned on and the switching tube S3 is turned off, the storage battery Bat charges the inductor L2, and the capacitor C3 charges the inductor L3; when the switching tube S2 is turned off and the switching tube S3 is turned on, energy in the storage battery Bat and the inductors L2 and L3 is supplied to the load R via the switching tube S3.

(4) An operating mode of photovoltaic cell PV separately supplying power to the load R:

In a case that none of the switching tube S1, the switching tube S2 and the switching tube S3 operate, when the switching tube S4 is turned on, the photovoltaic cell PV charges the inductor L1, and when the switching tube S4 is turned off, the photovoltaic cell PV and the inductor L1 simultaneously supply power to the load R.

The converter of the present disclosure can operate not only in a case that the voltage Vpv of the photovoltaic cell is greater than the voltage VB of the storage battery, but also in a case that the voltage Vpv of the photovoltaic cell is smaller than the voltage VB of the storage battery. The converter improves system stability and efficiency, and thus is applicable to scenarios of high power density.

FIG. 2 is an equivalent circuit diagram illustrating an operating process of the photovoltaic cell PV supplying power to the load R and charging the storage battery Bat according to the converter of the present disclosure; at this moment, the switching pipe S2 and the switching pipe S3 keep turned off, the photovoltaic cell supplies power to the load and the storage battery simultaneously, and duty ratios of two switching tubes S1 and S4, i.e., D1 and D4 respectively, as two independent control variables, control power transmission; as shown in this Figure, the voltage of the photovoltaic cell is represented as Vpv, the voltage of the storage battery is represented as VB, a voltage of the load is represented as V0, and based on the voltage-second balance characteristic of inductance, the relationship between the voltage Vpv of the photovoltaic cell, the voltage V0 of the storage battery, the voltage Vpv of the photovoltaic cell and the voltage VB of the storage battery can be concluded as follows:

$\begin{matrix} {V_{0} = {\frac{1}{1 - D_{4}}V_{PV}}} & (1) \end{matrix}$ $\begin{matrix} {V_{B} = {\frac{D_{1}}{1 - D_{1}}V_{PV}}} & (2) \end{matrix}$

The operating waveforms in this mode are shown in FIG. 6 . When the switching tube S1 and the switching tube S4 are both turned on, a current iL1 of the inductor L1 rises linearly, and a current iL2 of the inductor L2 and a current iL3 of the inductor L3 rise linearly in a reverse manner; when the switching tube S1 is turned off and the switching tube S4 continues to be turned on, the current of the inductor L1 continues to rise linearly, the inductor L2 charges the battery via freewheeling through the body diode of the switching tube S2, the current of the inductor L2 falls linearly in a reverse manner, the inductor L3 charges the capacitor C3 via freewheeling through the body diode of the switching tube S2, and the current of the inductor L3 falls linearly in a reverse manner.

FIG. 3 is an equivalent circuit diagram illustrating the operating process of the photovoltaic cell PV and a storage battery Bat jointly supplying power to the load according to the converter of the present disclosure, and at this moment, the switching tube S1 keeps turned off. The photovoltaic cell PV and the storage battery Bat simultaneously supply power to the load R, and by controlling the duty ratios of the switching pipe S2, the switching pipe S3 and the switching pipe S4, distribution control over input powers of two input sources is completed; the duty ratios of the switching pipe S2, the switching pipe S3 and the switching pipe S4 are represented as D2, D3 and D4 respectively, as shown in this Figure, the voltage of the photovoltaic cell is represented as Vpv, the voltage of the storage battery is represented as VB, the voltage of the load is represented as V0, and based on the voltage-second balance characteristic of inductance, the relationship between the voltage VB of the storage battery and the voltage of the load can be concluded as follows:

$\begin{matrix} {V_{0} = {\frac{D_{2}}{1 - D_{2}}V_{B}}} & (3) \end{matrix}$

In this mode, when the voltage Vpv of the photovoltaic cell is greater than the voltage VB of the storage battery, the operating waveforms are shown in FIG. 7 . When the switching tube S2 and the switching tube S4 are turned on, and the switching tube S3 is turned off, the inductor L1 is charged by the photovoltaic cell PV, the inductor L2 is charged by the storage battery Bat, the inductor L3 is charged by the capacitor C3, and currents of the inductors L1, L2 and L3 rise linearly; when the switching tube S2 and the switching tube S4 are both turned off, and the switching tube S3 is turned on, currents of the inductors L1, L2 and L3 fall linearly; when the switching tubes S4 and S3 are turned off and the switching tube S2 is turned on, the current of the inductor L1 continues to fall, and currents of the inductors L2 and L3 rise linearly.

When the voltage Vpv of the photovoltaic cell is smaller than the voltage VB of the storage battery and the duty ratio of the switching tube S2 is smaller than that of the switching tube S4, the operating waveforms are shown in FIG. 8 . When the switching tube S2 and the switching tube S3 are turned off, and the switching tube S4 is turned on, the photovoltaic cell PV charges the inductor L1, the current of the inductor L1 rises linearly, and the currents of the inductor L2 and the inductor L3 are zero; when the switching tube S2 and the switching tube S4 are turned on simultaneously, and the switching tube S3 continues to be turned off, the currents of the inductors L1, L2 and L3 rise linearly; when the switching tube S2 and the switching tube S4 are both turned off, and the switching tube S3 is turned on, currents of the inductors L1, L2 and L3 fall linearly.

FIG. 4 is an equivalent circuit diagram illustrating the operating process of a storage battery Bat separately supplying power to the load R according to the present disclosure. At this moment, the switching tube S1 and the switching tube S4 keep turned off, the storage battery Bat separately supplies power to the load R, and by controlling duty ratios of the switching pipe S2 and the switching pipe S3, distribution control over input powers of the storage battery is completed; duty ratios of the switching pipe S2 and the switching pipe S3 are represented as D2 and D3 respectively, as shown in this Figure, the voltage of the storage battery is represented as VB, the voltage of the load is represented as V0, and the relationship between the voltage of the storage battery and the voltage of the load concluded based on the voltage-second balance characteristic of inductance is shown in Formula (3).

The operating waveforms in this mode are shown in FIG. 9 . When the switching tube S2 is turned on and the switching tube S3 is turned off, the storage battery Bat charges the inductor L2, the capacitor C3 charges the inductor L3, and currents of both the inductor L2 and the inductor L3 rise linearly. When the switching tube S2 is turned off, the switching tube S3 is turned on, the storage battery, the inductor L2 and the inductor L3 jointly supply power to the load, and the currents of the inductor L2 and the inductor L3 fall linearly.

FIG. 5 is an equivalent circuit diagram illustrating the operating process of the photovoltaic cell PV separately supplying power to the load R according to the present disclosure. At this moment, the switching tube S1, the switching tube S2 and the switching tube S3 keep turned off, the photovoltaic cell PV separately supplies power to the load R, and by controlling a duty ratio of the switching pipe S4, distribution control over input power of the photovoltaic cell is completed; the duty ratio of the switching pipe S4 is represented as D4, and as shown in this Figure, the voltage of the photovoltaic cell is represented as Vpv, the voltage of the load is represented as V0, and the relationship between the voltage of the photovoltaic cell and the voltage of the load concluded based on the voltage-second balance characteristic of inductance is shown in Formula (1).

The operating waveforms in this mode are shown in FIG. 10 . When the switching tube S4 is turned on, the photovoltaic cell PV charges the inductor L1. In a case that the current of the inductor L1 rises linearly, when the switching tube S4 is turned off, the photovoltaic cell PV and the inductor L1 simultaneously supply power to the load R, and the current of the inductor L1 falls linearly.

The above displays and describes the basic principles, main features and advantages of the present disclosure. The components described herein are common technologies in the conventional art. It should be understood by those skilled in the art that, the present disclosure is not limited by the aforementioned embodiments, and the aforementioned embodiments and the description only illustrate the principles of the present disclosure. Various changes and modifications may be made to the present disclosure without departing from the spirit and scope of the present disclosure, and such changes and modifications shall fall within the claimed scope of the present disclosure. The protection scope of the present disclosure is defined by the appended claims and their equivalents. 

What is claimed is:
 1. A three-port converter with a wide input range, comprising: a photovoltaic cell (PV) having a positive electrode and a negative electrode, a storage battery (Bat) having a positive electrode and a negative electrode, a resistance load R, a boost circuit (Boost) configured to connect the photovoltaic cell PV and the resistance load R, and a reversible boost-buck circuit (Sepic-Zeta) configured to connect the photovoltaic cell PV, the storage battery (Bat) and the resistance load R; wherein in the boost circuit (Boost), the positive electrode of the photovoltaic cell PV is connected to an end of a capacitor C₁ and an anode of a diode VD₁, an anode of a diode VD₂ is connected to an end of an inductor L₁, and a drain of a switching tube S₄ and an anode of a diode VD₄ are connected to an other end of the inductor L₁; a cathode of the diode VD₄ is connected to an end of an output filtering capacitor C₄ and an end of the resistance load R; wherein in the reversible boost-buck circuit (Sepic-Zeta), the positive electrode of the storage battery (Bat) is connected to an end of a capacitor C₂ and an end of an inductor L₂, a drain of a switching tube S₂ and an end of a capacitor C₃ are connected to an other end of the inductor L₂, three branches are led out from an other end of the capacitor C₃ with a first branch connected to a source of a switching tube S₁, a second branch connected to a drain of a switching tube S₃, and a third branch connected to an end of an inductor L₃, a series circuit of the switching tube S₁ and the diode VD₂ is connected to a cathode of the diode VD₁ and the end of the inductor L₁, and a series circuit of the switching tube S₃ and a diode VD₃ is connected to the other end of the inductor L₂ and the anode of the diode VD₄; and the cathode of the diode VD₄ is connected to the end of the output filtering capacitor C₄ and the end of the resistance load R; and an other end of the resistance load R is connected to an other end of the output capacitor C₄, a source of the switching tube S₄, an other end of the inductor L₃, a source of the switching tube S₂, the other end of the capacitor C₂, the negative electrode of the storage battery Bat, an other end of the capacitor C₁, and the negative electrode of the photovoltaic cell (PV).
 2. The three-port converter with the wide input range according to claim 1, wherein the photovoltaic cell (PV) and the storage battery (Bat) are connected via the reversible boost-buck circuit (Sepic-Zeta), such that a nonisolated three-port direct-current switching converter operates not only in a case that the voltage V_(pv) of the photovoltaic cell is greater than the voltage V_(B) of the storage battery, but also in a case that the voltage V_(pv) of the photovoltaic cell is smaller than the voltage V_(B) of the storage battery.
 3. The three-port converter with the wide input range according to claim 1, wherein the resistance load R is provided with three ports.
 4. The three-port converter with the wide input range according to claim 3, wherein the photovoltaic cell (PV) and the storage battery (Bat) are connected via the reversible boost-buck circuit (Sepic-Zeta), such that a nonisolated three-port direct-current switching converter operates not only in a case that the voltage V_(pv) of the photovoltaic cell is greater than the voltage V_(B) of the storage battery, but also in a case that the voltage V_(pv) of the photovoltaic cell is smaller than the voltage V_(B) of the storage battery.
 5. A control method of a three-port converter with a wide input range, wherein the control method comprises following four operating modes: (1) an operating mode of a photovoltaic cell (PV) supplying power to a resistance load R and charging a storage battery (Bat): in a case that neither a switching tube S₂ nor a switching tube S3 operates, when a switching tube S₁ and a switching tube S₄ are turned on, the photovoltaic cell (PV) charges the storage battery (Bat) via a capacitor C₃ and an inductor L₂, and charges the inductor L₂ and an inductor L₃; when the switching tube S₁ is turned off and the switching tube S₄ continues to be turned on, the photovoltaic cell (PV) continues to charge an inductor L₁, the inductor L₃ charges the capacitor C₃, and the inductor L₂ supplies power to the resistance load R via freewheeling through a body diode of the switching tube S₂; when both the switching tube S₄ and the switching tube S₁ are turned off, the photovoltaic cell (PV) and the inductor L₁ supply power to the resistance load R, the inductor L₃ continues to charge the capacitor C₃, and the inductor L₂ continues to supply power to the resistance load R via freewheeling through the body diode of the switching tube S₂; (2) an operating mode of the photovoltaic cell (PV) and the storage battery (Bat) jointly supplying power to the resistance load R: when a voltage V_(pv) of the photovoltaic cell is greater than a voltage V_(B) of the storage battery, the switching tube S₁ does not operate, and the switching tube S₂ and the switching tube S₃ are turned on complementarily; when the switching tube S₂ is turned on and the switching tube S₃ and the switching tube S₄ are turned off, the photovoltaic cell (PV) and the inductor L₁ supply power to the resistance load R, the storage battery Bat charges the inductor L₂, and the capacitor C₃ charges the inductor L₃; when the switching tube S₂ continues to be turned on, the switching tube S₃ continues to be turned off, and the switching tube S₄ is turned on, the photovoltaic cell (PV) charges the inductor L₁, the storage battery (Bat) continues to charge the inductor L₂, and the capacitor C₃ continues to charge the inductor L₂; when the switching tube S₃ is turned on and the switching tube S₂ and the switching tube S₄ are turned off, the photovoltaic cell (PV) and the inductor L₁ supply power to the load, the storage battery (Bat) and the inductor supply power to the resistance load R via the capacitor C₃, and the inductor L₃ also supplies power to the resistance load R; when the voltage V_(pv) of the photovoltaic cell (PV) is smaller than the voltage V_(B) of the storage battery and a duty ratio of the switching tube S₂ is smaller than that of the switching tube S₄, the switching tube S₁ does not operate; when the switching tube S₄ is turned on and the switching tube S₂ and the switching tube S₃ are turned off, the photovoltaic cell (PV) charges the inductor L₁; when the switching tube S₄ continues to be turned on, the switching tube S₃ continues to be turned off, and the switching tube S₂ is turned on, the photovoltaic cell (PV) continues to charge the inductor L₁, the storage battery (Bat) charges the inductor L₂, and the capacitor C₃ charges the inductor L₃; when the switching tubes S₂ and S₄ are turned off and the switching tube S₃ is turned on, the photovoltaic cell (PV) and the inductor L₁, the storage battery (Bat) and the inductors L₂ and L₃ supply power to the load simultaneously; (3) an operating mode of the storage battery (Bat) separately supplying power to the resistance load R: in a case that neither the switching tube S₁ nor the switching tube S₄ operates, the switching tube S₂ and the switching tube S₃ are turned on complementarily, and input power of the photovoltaic cell (PV) is zero; when the switching tube S₂ is turned on and the switching tube S₃ is turned off, the storage battery (Bat) charges the inductor L₂, and the capacitor C₃ charges the inductor L₃; when the switching tube S₂ is turned off and the switching tube S₃ is turned on, energy in the storage battery (Bat) and the inductors L₂ and L₃ is supplied to the resistance load R via the switching tube S₃; and (4) an operating mode of the photovoltaic cell (PV) separately supplying power to the load R: in a case that none of the switching tube S₁, the switching tube S₂ and the switching tube S₃ operate, when the switching tube S₄ is turned on, the photovoltaic cell (PV) charges the inductor L₁, and when the switching tube S₄ is turned off, the photovoltaic cell (PV) and the inductor L₁ simultaneously supply power to the resistance load R. 